Làm thế nào để thay đổi kết cấu trên dulce de leche?

I recently made dulce de leche using the can in boiling water method. It came out tasting delicious but it was way to runny. I boiled it for two hours and used sweetened condensed milk and was expecting something that would be able to hold up a spoon. Instead, it was more like a thin sauce. Anyway how do I fix this? or is this the way that it is supposed to come out?

The texture is controlled simply by time; 2 hours isn't enough. Try 3 to 4 hours. Or use a pressure cooker, it goes much faster in there - about 45 minutes should do it.